Soil and Forage Analysis

by Carole Youngs

Alternative Forage

grass-field

Although Green Farm is not registered organic, we try as far as possible to ensure that all our activities follow organic principles, especially in the rearing of our lambs.  Apart from a small amount of creep feed at weaning, to counteract the stress of being separated from their dams, lambs are reared on forage alone.  This means our grassland (from which we also cut hay to provide conserved forage through the winter months) has to provide all the nutrients that are essential for strong growth.  Importantly, we want to ensure that most of our lambs intended for slaughter will be finished within 20 weeks to ensure we don’t put pressure on our limited pastures beyond the summer growing season.  So, our grass is very important to us and during the seven years since we came to the farm, we’ve added quite a lot of ‘alternative’ forages to improve our existing species-rich permanent pastures.  These include:

  • White clover – for its nitrogen-fixing ability which adds fertility to the soil, and its root structure that makes it both drought-tolerant and improves the structure of the soil (red clover is also useful, but it produces oestrogens that can interfere with a ewe’s fertility, so should be avoided on pastures used for ‘flushing’);
  • Chicory (Puna II variety) – with a very long tap-root, chicory is not only drought tolerant, but also provides a rich source of minerals that aren’t available to shallower-rooting plants, combined with a leafy, high protein forage which also has proven anthelmintic qualities, meaning a significant reduction in our use of chemical wormers;
  • Plantain – good drought tolerance, highly palatable and provides a good source of minerals and trace elements.

clover_chicory_plantain
Images courtesy of Cotswold Seeds

During years with exceptionally low rainfall , grass growth during the summer months can be severely restricted.  But, I wondered, is it only the lack of moisture that is inhibiting growth, or are there perhaps other factors involved?  More specifically, is our soil structure and composition able to provide the essential elements for grass growth: namely air, moisture and a complex cocktail of minerals and trace elements?

I know from having dug our vegetable plot single-handedly that our soil texture is variously heavy clay with a good mix of riverbed silt (I found loads of smooth riverbed pebbles and softer mudstone with embedded fossils), and its structure is quite ‘blocky’, meaning that it’s naturally quite stable – good so far.  However, if the ground becomes compacted, and clay soils are the ones most likely to do so, it means there will be less space between the blocks for air, water and root development.

Soil Analysis

So, under the guidance of Ray, our Consultant Agronomist, we carried out a compaction test on three fields that I had identified as performing less well than they might … this involved some pretty technical kit, namely a spade and a penetrometer!  A clod of earth was dug from each field, and here is a brief summary of the results (the full report was 10 pages!):

RICKYARD

Closest to house, sheep & horse grazing

Red, loamy topsoil, well-rooted and friable to 5cm with a good number of worms observed, below this zone soil increasingly structured with limited root penetration; vertical cracking increases water holding capacity

FAR ORCHARD

Sheep & horse grazing

Red brown loamy topsoil, deep (10cm) and well-rooted; moderate earthworm activity

SEED PIECE

Sheep grazing & hayfield (so traversed by heavy equipment), muck spread annually in Spring

Sward in good condition, dark brown loamy topsoil loose, well-rooted and friable, root growth observed to 25cms (of the 3, this field is the only one that we spread FYM – farmyard manures – onto, which explains the high level of organic matter in the soil)

soil-analysis

Essentially, his recommendations included regular assessment of soil (which, as we are in an NVZ – nitrate vulnerable zone – we have to do annually), aerating specific areas in Rickyard and Far Orchard, and removing livestock in wet conditions (not easy with limited acreage!), all of which would potentially improve grass production by up to 30%.  Finally, as an interesting aside, he calculated that our flock of 35 sheep and 2 large horses would between them produce 105m3 of muck annually, with an estimated commercial value in the region of £400.  I don’t feel so bad about buying that new bridle now, paid for by poo!

Next is the science bit, which all you good gardeners will be sagely nodding at! 

Ray set off on a hike around the fields with his sampling auger to collect a number of soil samples for laboratory analysis.  A couple of weeks later we all sat around the kitchen table while he patiently explained the Analytical Report.  Starting with the easy bit, the soil acidity, or pH value that, in an ideal field, will be between pH6– pH6.5 (with 1 being very acidic, 7 being neutral and 14 being very alkaline).  Ours is slightly acid, ranging from pH6.21to pH6.4, so far so good!

Potassium or Potash (K) enables the plant to efficiently transport nutrients from root to leaf.  It’s an expensive element, so I was pleased to note that in all but one part of our hayfield, we have relatively high amounts in our soil (Index 3).  Too high a level, which will cause lush grass growth, can interfere with a ruminant’s ability to absorb magnesium and cause fatal ‘staggers’ at or around lambing and calving, so if you need to apply K, don’t do it at this time.

Next, we looked at some rather surprising Phosphorus (P) results.  Phosphorus (or phosphate) is essential for plant root development and thus the efficient use of nitrogen in the soil, so it’s one of the most important elements in plant growth, but as with all elements, you can have too much or too little of a good thing.  In our case it is considerably too little (Indices 1-2), but this is to some extent mitigated by our slightly acid soil, which means that what P there is, is readily available to the plants that need it.  Alkaline soils can create a ‘lock-up’ or ‘antagonistic’ effect meaning that P is not available to plants.   Too much P can also create an environmental problem as it can leach into waterways and cause toxic algal blooms.

But the real surprise came with the Magnesium (Mg) results, which were right at the top of the scale (Index 7).  Oh good, I thought, that means our sheep won’t suffer from Magnesium Staggers.  Wrong again … on the ‘too much of a good thing’ principle.  Too much Mg reduces the availability of K and N, and locks up calcium in the soil making it ‘claggy’ and hard to cultivate.  In fact, our K and Mg levels are completely the wrong way around!  Ours are on a ratio of 1:1.5 and the ideal would be 3:1.

Finally we looked at Nitrogen (N) and Sulphur (S), both major nutrients necessary for plant growth, and existing in our soil at moderate levels (with the N at very good levels where we have high proportions of clover in the grass sward) which need to be topped up in the correct amount, from the right source, at the right time.

All of this left me thinking I wish I’d paid more attention in my Chemistry lessons at school, and I would recommend that anyone considering a career on the land studies this subject seriously – it’s the ‘building blocks’ of all growth, plant and animal!  Thankfully for me, people like Ray exist, and the over- and under-supplies of nutrients can be quite simply, cheaply (and organically) remedied.  On his advice, in addition to our regular muck spreading and harrowing in the spring, we will also be adding gypsum (Calcium Sulphate) every 4/5 years, which will both help our soil structure through a process known as flocculation, as well as helping mitigate the high levels of Magnesium.

There’s just one other factor that we need to consider, and that is to recognise that haymaking removes considerable amounts of nutrients from the field, whereas fields used for grazing animals don’t suffer this depletion effect as the animals recycle the elements in their dung and urine.

So, that’s my version of agronomy; not an easy subject, but one that is really important.  By having the most nutritious grazing in front of them, we ensure that our livestock flourish – and by making sure that they have access to vital nutrients from our grassland, we make sure that our lambs grow on unchecked.

grasses

Forage Analysis

Now to state the obvious:  knowledge is of no use unless you put it into practice!  So, in the knowledge that one of the most important aspects of a successful lambing is ewe nutrition, I sent a sample of our hay away for analysis.  As hay is the basic winter forage we feed our ewes during their pregnancy, I wanted find out whether it lacks any micro-nutrients that are essential to both maintain a healthy pregnancy, and produce bouncing lambs with the least intervention from me!  In past years we’ve provided the ewes with ‘mineral buckets’ from flushing through to lambing as an ‘insurance’ against any shortages, and we’ve also used mineral and trace element drenches to good effect – but this is an expensive and quite possibly wasteful strategy!

ewe-eating-hay

Many feed and supplement companies offer a free forage analysis service (for hay, haylage and silage) – on the basis that most forage lacks some essential elements which you will have to supplement by buying their products!  So it’s worth asking if they offer a service – and even if you do have to pay for an analysis, it can quickly pay you back.  If your forage is really good quality, you will be able to feed less concentrates, and with the price of bagged feed (and mineral buckets) rising all the time, this can result in a considerable saving.

You might think that having had the soil tested it’s not worth testing the forage, as surely this will reflect what’s in the soil (if you make your own forage).  Unfortunately, this isn’t the case as some elements have an ‘antagonistic’ effect on others, an interactive effect that locks up certain trace elements so they are not available to grazing animals.  Additionally, some elements will be unavailable to shallow roots, which is why adding deep-rooting forages such as plantain and chicory to your grazing pastures can make a very economical difference!

grass-field

The results of our hay analysis were quite an eye-opener – every single essential mineral and trace element (except the antagonists, highlighted) was below the guidelines for ruminants, and some were significantly lacking:

Mineral /

Trace Element

%age of requirement

Nutritional Role

Sodium

50%

Palatability; electrolytic effect – hydration; bone development; muscle function

Phosphorus

30%

Bone development; muscle function; energy production

Calcium

60%

Bone development; muscle function; has a role in absorption of zinc

Magnesium

80%

Bone development; muscle function; activates enzymes

Selenium

20%

Ewe fertility; lamb survival (immunity to disease and vigour)/birth weight; DNA function; male fertility; helps metabolise iodine to protect muscles from damage (‘white muscle disease’) in lambs; aids ‘cleansing’ and milk yield in ewes;

Iodine

30%

Formation of hormones (eg. thyroxine); essential for newborn lamb to maintain body temperature

Cobalt

50%

Implantation & early foetal development; lamb vigour/appetite; used in the rumen to produce vitamin B12 which promotes wool growth (deficiency is called ‘Pine’)

Copper

20%

A tricky one with sheep, as an under-supply can cause swayback in lambs, while an over-supply can be toxic (especially in Texels and North Ronaldsay); influences effect of iron in haemoglobin synthesis

Zinc

40%

Essential for skin and hoof growth; helps prevent mastitis

Manganese

70%

Anti-oxidant; essential for carbohydrate and lipid synthesis – lamb growth & vigour

 

 ANTAGONISTS

Iron

130%

An excess will reduce availability of copper

Potassium

90%

Bone development; muscle function

Sulphur

110%

Reduces availability of copper, but essential for bone development & muscle function

Molybdenum

190%

Reduces availability of copper; in excessive amounts can cause diarrhoea, infertility, low birth weight, retarded growth

 

So, I obviously need to supplement the fodder to supply all the micronutrients needed by my ewes in the run up to lambing in mid-April.

 


 

For further information, please see the DVD 'Managing Your Flock for Peak Health'

 


 

The above article is taken from the Farm Diary, December 2011 and January 2012

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